It has been found that the output of seed from alfalfa is greatly increased if the alfalfa is pollinated by insects and the insect most effective for pollination of seed alfalfa is the leafcutter bee. While the leafcutter bee occurs naturally in several areas of the Western United States, domestication of the bee is in wide practice today and requires the construction of artifical nests to increase the number of bees that are present in a given area. In the construction of such nests or hives the following factors must be considered: (1) initial cost, (2) ease of cleaning and larvae removal, (3) resistance to predators and parasites. By balancing and optimizing the above factors, an economically practical nest may be constructed.
Low cost of construction of leafcutter bee nests is essential in that a large number of nests must be provided for fields of even moderate size. Since the leafcutter bee is gregarious and nests in holes in many materials, a nest of very low initial cost has been constructed by simply drilling a plurality of holes of the proper depth in wooden blocks. The female bee partitions the holes into several cells and lays an egg in each cell. The optimum depth of these holes has been found to be approximately four inches, which results in the last or lowest three cells in the hole containing female eggs--the female bee only being responsible for pollination of alfalfa. Similar low cost nests have been constructed from boxes of paper drinking straws or grooved boards held in frames. Nests of these types are generally discarded at the end of each season because of their initial low costs and because of the difficulty in cleaning. Nests of higher initial cost are justifiable only if the nest is reusable within the season and from season to season. For the above reasons, the current trend in the construction of leafcutter bee nests has been toward synthetic materials that are reusable in spite of their somewhat greater initial cost.
The second factor mentioned, i.e., ease of cleaning and larvae removal, has become more important with the increase in demand for bee pollination of alfalfa. In general, after the eggs have been hatched and the young bees have left the nest, the cells of the nest are still filled with debris which may be removed to prevent the growth of fungus and to make way for new nesting holes. Such means as sandblasting and mechanical devices for scraping the interiors of the cells in nests constructed of grooved boards, for example, have been developed. The development of mechanical cleaning means has led to the practice of removing immature larvae from the cells and incubating the larvae under artificial heat. The incubation of the larvae allows control of pests and also allows a larger number of generations of bees to be propagated from a given number of nests in a given season. A mechanical nest cleaning and larvae removal apparatus for nests of the spirally wound type is illustrated in my copending U.S. patent application filed concurrently herewith.
The final factor, that of resistance to predators and parasites, is perhaps the most important. The nests may be attacked by a number of predators which include rodents, as well as insects which burrow into and can destroy the nest itself. Destruction of the physical materials of the nest also destroys the developing bees within the cells with the nest destroyers frequently eating immature leafcutting bees. Insecticides are generally impractical for use in controlling this type of predation due, of course, to the possibility of injury to the leafcutter bees themselves. One of the most destructive insect parasites is a small wasp (Monodontomerus obscurus) which lays eggs in the cells of the leafcutter bee nests, which hatch into larvae that destroy the developing leafcutter bee larvae. The wasp generally attacks the hindmost cell of the nest from behind and can therefore destroy as much as one-third of the useful production of the bees, i.e., the female larvae. A nest should therefore be preferably impenetrable to these types of predators and parasites.